This is very interesting.Yes, when the screen shuts off sometimes I have to unplug the cable from the back and plug it back in. I've opted to use a display cable as that's what I had lying around at the time.
I don't think it's an issue with the video out though. I believe it's an issue with the USB port. Seems to go away if I use a wired mouse and keyboard.
I noticed that unplugging the power and waiting, then plugging it back in fixes it.
I also use a wireless logitech keyboard.
Are you saying using displayport fixed all your issues?
Edit: Hmm, Quango might be right, I had already tried another hdmi cable but I tried another one again and things fixed themselves, at least for now.